A female boa constrictor snake has given birth to two litters of extraordinary offspring. Evidence suggests the mother snake has had multiple virgin births, producing 22 baby snakes that have no father. More than that, the genetic make-up of the baby snakes is unlike any previously recorded among vertebrates, the group which includes almost all animals with a backbone.
…
“All offspring are female. The offspring share only half the mother’s genetic make-up,” he told the BBC.
…
Humans for example have X or Y sex chromosomes; females have two X chromosomes and males have a combination of an X and a Y chromosome. In place of X and Y, snakes and many other reptiles have Z and W chromosomes.

In all snakes, ZZ produces males and ZW produces females. Bizarrely, all the snakes in these litters were WW. This was further proof that the snakes inherited all their genetic material from their mother, as only females carry the W chromosome.

“Essentially they are half clones of their mother,” says Dr Booth. That is because the baby snakes have inherited two copies of one half of their mother’s chromosomes, including one W chromosome.
…
More astonishing though, is that no vertebrate animal in which the females carry the odd sex chromosome (in this case the W chromosome) has ever been recorded naturally producing viable WW offspring via a virgin birth.

“For decades WW has been considered non-viable” says Dr Booth. In such species, all known examples of babies that are the product of parthenogenesis are male, carrying a ZZ chromosomal arrangement.